100% for safety. Which includes "safety" to the equipment.
As for vehicle positive grounds, I have seen many while I was working. Fire engines, fire trucks, etc. But I didn't know the age of these vehicles.
But I know of no cars, motorcycles or RVs that use a positive ground. But I do know some EVs, such as my Zero motorcycles do NOT use a ground at all. Not even on the 12 volt lights after the DC2DCC. Uses a "floating ground", which means a common wire. Cannot use the frame for a negative wire on a voltmeter to anything. So I use the headlamp low side to check voltages.
I think EVs with a metal frame make sure there is no possible return path to ground in case metal tools need to be needed to pry somebody out after an accident. Not really needed on a motorcycle where such cannot apply. Perhaps is a law and they didn't make an exception for motorcycles, but I really don't know.
-Don- Auburn, CA